This invention relates generally to temperature sensors for heating ovens.
Temperature sensors conventionally employed in electronically controlled ovens such as sheathed nickel wire sensors or platinum resistance temperature detectors are characterized by a relatively low thermal coefficient of resistivity, which limits the accuracy of such devices. Commonly assigned, co-pending patent application Ser. No. 462,110, filed Jan. 8, 1990, discloses an improved multi-element sensor employing a glass-ceramic substrate characterized by a higher coefficient of resistivity. The resistance of the glass-ceramic substrate is used to measure temperature over the middle and upper portion of the operating range. However, the resistance of the substrate becomes too large for use for temperatures in the lower portion of the operating range. The resistance of a serpentine length of conductive material deposited on the substrate is used to measure temperature over the low end of the oven operating range. This multi-element sensor provides a significant performance advantage over prior art sensors particularly in the mid to upper portion of the temperature range. In addition sensors of this type are operable over an extended temperature range up to 1500 F. One disadvantage is that the thermal inertia of the glass-ceramic material renders the sensor slow to respond to changes in temperature.
It is therefore an object of the present invention to provide an improved temperature sensor for a cooking oven which retains the accuracy advantages of the aforementioned glass-ceramic sensor while being lower in cost and having a greater speed of response to changes in temperature.